Thanks,

The problem is that I don't want to restart the application !

If I do this :

addDockWidget(static_cast<Qt:ockWidgetArea>(1), ui.dockWidget_left);
ui.dockWidget_left->raise();
ui.dockWidget_right->setFloating(false);
ui.dockWidget_left->show();

Everything works... I only redisplay them as docked at the default place.

Thanks for your help